1. Field of the Present Invention
The present invention relates to a development apparatus and an image formation apparatus comprising such development apparatus.
2. Description of Related Art
In a type of image formation apparatus using an electrographic system, for example, a development method in which, with the use of two-component developer composed of toner and carrier, the friction-charged toner is carried to a development area by an appropriate stirring means, and the toner is absorbed on an electrostatic latent image formed on a latent image carrying member for forming a toner image, is used. In such development method with the use of two-component developer, in order to maintain even toner density in the developer, new toner is replenished according to toner consumption amount.
In such image formation apparatus, it is required to obtain more high-quality images. In response to the request, for example, toner having small particle diameter has been used. Further, in connection with the toner having smaller particle diameter, particle diameter of the carrier is also requested to become smaller.
Accordingly, while it is possible to form high-quality images with the use of toner having small particle diameter and carrier having small particle diameter, it is difficult to sufficiently stir developer due to the decrease of flowability of the developer itself. As a result, the newly replenished toner is supplied to the development area without reaching to a state of having predetermined electrostatic charging amount, and thereby there is a problem such as toner fog and toner blurring easily happening.
And such problem frequently happens when an image with high dot area percent is continuously output such as a case of forming a color image.
On the other hand, these days, in conjunction with the increase of social consciousness regarding environmental safeguard, for example, resource saving, such as toner recycling or the like, has been attempted.
However, since toner collected after once having been used for development has inferior electrostatic charging characteristic to unused toner, there is a problem of toner fog and toner blurring due to insufficient toner electrostatic charging amount.
According to such problem, conventionally, a number of arts improving stirring efficiency of developer have been proposed. For example, structuring to have a stirring means having high developer carrying capability with a member serving as an auxiliary stirring member has been proposed (see Japanese Patent Application Publications (Unexamined) Nos. Tokukai-Hei 7-13420, Tokukai-Hei 9-166918 and Tokukai-Hei 9-288412).
However, in any of the above-mentioned arts, while stirring efficiency of developer is improved, circulation carrying speed of developer in the development apparatus decreases. As a result, toner density of developer supplied to the developer carrying member with respect to a rotation axis direction of the developer carrying member becomes uneven, and, in particular, when an image having high dot area percent is to be output continuously, it is easy that image density unevenness significantly happens, and thereby there is a problem that it is difficult to securely form a high-quality image.
As mentioned, if one tries to prevent the occurrence of toner fog and toner blurring by improving stirring capability of developer so as to make replenished new toner have sufficient electrostatic charging amount, there is a problem that it becomes easy that image density unevenness happens due to the decrease of carrying capability of developer. Consequently, the actuality is, it is difficult to solve two problems at the same time, the two problems that the occurrence of toner fog and toner blurring, and the occurrence of image density unevenness.